Military personnel commemorate the millions of men and women from around the Commonwealth who served during the first world war. Photograph: Russell Cheyne/PA

A little over a year ago Kirsten Fell, then a 15-year-old schoolgirl from Dunbar grammar school in East Lothian, went on a school trip to the battlefields of Flanders and visited a cemetery where 81% of the dead had never been identified.

Each pupil was asked to stand in front of one of the graves and imagine the soldier who lay there – his name, appearance and personality – before laying a poppy.

"As I laid my poppy on the headstone of my soldier and gazed out over the never-ending ripples of white stones, I suddenly felt so small," Kirsten wrote after returning to Scotland. "My outlook on life has never been the same, " Kirsten wrote after returning to Scotland.

On Monday, a congregation at Glasgow Cathedral including Prince Charles, David Cameron, political and military leaders and dignitaries from around the Commonwealth heard the schoolgirl, now 16, describe the obligation she feels, not only to that unnamed soldier but also to the family unable to mourn him.

"If I remember," she said, "then I have done well and done my duties to those who loved him but have never been able to visit. I did it for them and didn't only pay my respects, but theirs too."

Less than 12 hours earlier, Glasgow had been celebrating the close of the Commonwealth games with a lively ceremony at Hampden Park. The contrast between that event and the solemn service in the city's austere medieval cathedral could not have been more stark.

But it was fitting, given the celebration of Commonwealth sport that has convulsed Glasgow over the past fortnight, that it was this city that was chosen to host an event honouring not only the 761,000 young British men who died in the conflict but also the many tens of thousands from what were then dominions of the British crown.

The school trip had been hugely emotional, the teenager told the Guardian, and she and her friends still talked about what they had seen. It was "really important" that young people were involved in commemorating the first world war dead, she said.

"The soldiers were so young, they were the same age as us. We could really relate to them." She hopes one day to visit the grave again. "It's the fact that those soldiers were unknown, and their families will never know where they are."

The schoolgirl was not the only speaker in Glasgow to stress the connection they felt to the fallen.

Private Dillon Rae of the 52nd Lowland, 6th Battalion of the Royal Regiment of Scotland had been invited to read an extract from the diary of another young Scottish private, Arthur Honeyball, who had been sent to the front with the 1st Cameronians of the war in the early months.

On 1 September, 1914, Honeyball's commanding officer, Captain Ronald Rose, wrote an account of one particularly ghastly day, which was read by a captain from Rae's battalion: "The enemy got their guns up unobserved and fired on the L battery. They have been cut to pieces. We manage to get back a bit … on the way we pass the place where the deed was done. It is like a little corner of hell. They are shooting the wounded horses. The men have been removed. The road is covered with blood trails."

Seven weeks later, Rose made an appearance in Honeyball's own journal. "Twenty-second October 1914 … My platoon retired to a barn, and we placed the wounded behind a haystack. Captain Rose said that he would see where we could retire to next time, and as he looked round he was shot in the back. I asked him where he had got it, he said in the back, as soon as he said that, he got another that killed him.

"I had got hold of him by the feet, and the other chap had got hold of his shoulders. And then I got mine in the thigh. I must have fainted after that, because when I came to my senses I was in a ditch …"

Rae, whose company inherited the Cameronians badge after the disbandment of the original regiment, said it was "a huge honour" to have been asked to speak. Appearing in his regimental kilt, polished boots and spats, the young reservist retold Honeyball's story in a Glaswegian brogue probably very like that of his predecessor a century ago.

Reading Honeyball's words had "kind of brought it to life", Rae said. He served in Helmand in 2008 and 2010, and for those in his position, he said, remembrance was not something confined to ceremonies. "I have a lot of military pride. I don't just need an anniversary to remember. It's something I think about most days."

A schoolgirl's tribute

Kirsten Fell is a 16-year-old pupil at Dunbar grammar school. In May 2013 she went with her school to the Flanders battlefields. This is an extract from a piece of reflective writing she composed on her return describing the experience, which she read at Glasgow Cathedral:

"The experience began when we marched on to the bus. From then on we were following the footsteps of the soldiers of World War 1. No technology, no contact with families or the outside world. Just us. And the battlefields.

The graves lay silent – there was peace. Every man with his own story – no man was the same but they all died and lie side by side – together.

'Known unto God' – a phrase seen, heard and read too many times – A soldier known unto God – No name – No visitors – Just one of thousands and thousands who lie in the vast cemeteries of the first world war.

Poelkapelle [cemetery] is just one, but 81% of the thousands of soldiers who live there are 'known unto God'. 81% are unknown. 81% are unidentified. 81% will never be visited by their loved ones as their families will never know where they lie or what happened to them.

We were each placed before a headstone – a headstone of an unknown soldier. We were told to imagine what this soldier had been like and give him a name, an appearance and a personality. Once we had done that we were told to take a few minutes to remember. There is one thing that is associated with remembrance, one flower, the poppy.

As I laid my poppy on the headstone of my soldier and gazed out over the never-ending ripples of white stones, I suddenly felt so small. So tiny. From then on my outlook on life has never been the same.

My soldier lay in Poelkapelle cemetery. He still does and will always lie in Poelkapelle. But if I remember – and my poppy stays with him and is loyal – then I have done well and done my duties to those who loved him but have never been able to visit. I did it for them and didn't only pay my respects but theirs too.

They told us we would change. They were right. We will never be the same again. I didn't want to go. I didn't want to forget. But the truth is you don't. You never forget something that has meant so much to you and after experiencing something as powerful. It will never go.

It will always be with me and nothing will be forgotten. I will remember my soldier. Forever."